Fine materials generated from mining activities are often found well-dispersed in aqueous environments, such as wastewater. The finely dispersed materials may include such solids as various types of clay materials, recoverable materials, fine sand and silt. Separating these materials from the aqueous environment can be difficult, as they tend to retain significant amounts of water, even when separated out, unless special energy-intensive dewatering processes or long-term settling practices are employed.
An example of a high volume water consumption process is the processing of naturally occurring ores, such as coal and oil sands. Naturally occurring ores are heterogeneous mixtures of hydrophobic organic molecules or materials and solid inorganic matter. During the processing of such ores, colloidal particles, such as clay and mineral fines, are released into the aqueous phase often due to the introduction of mechanical shear. In certain embodiments, this shear is associated with the hydrocarbon-extraction process. In addition to mechanical shear, alkali water is sometimes added during extraction, creating an environment more suitable for colloidal suspensions. A common method for disposal of the resulting “tailing” solutions, which contain fine colloidal suspensions of clay and minerals, water, sodium hydroxide and small amounts of remaining hydrocarbon, is to store them in “tailings ponds”. These ponds take years to settle out the contaminating fines, making the water unsuitable for recycling.
As an alternative, we have developed alternative technologies to treat tailings so that they are separated into a solid phase and a liquid phase, as disclosed in PCT/US09/54278, the entire teachings of which are hereby incorporated by reference. After this separation, they can coexist in a semisolid, semifluid slurry until they are transported to their final destination. The formed solids need to be disposed of by beaching or other means of deposition.
During the transport process to its place of deposition, the mechanical properties of the slurry become important, especially shear resistance. For example, the high rate of fluid flow during transport can cause shear stress to be applied to the solid materials in suspension. Methods for tailings treatment such as coagulation and flocculation may not survive these mechanical stresses, and the solid aggregates can degrade, forming a stratified deposit of sand and fines while resuspending some fine in any remaining water. Commonly, to transport the formed solids or slurries containing them centrifugal pumps or positive displacement pumps may be used. Such pumps can exert shear on the solids, so that they break apart under such stresses. If the solid responds to the shear stress by regenerating fines, or if the solid segregates into layers (e.g., with a top-most layer containing more fines and the lower layers containing more sand), then the desired separation of the slurry into a recyclable water component and a reusable solid component will not be accomplished. Therefore, a need exists for a process that can withstand stresses such as pumping and high-flow, high-shear transport systems while producing the desired geotechnical properties in the separated tailings when they are deposited.